1. Field of the Invention
The present invention relates generally to implantable devices, examples of which include stents and grafts. More particularly, the present invention is directed to a method of coating an implantable device having a plurality of depots formed in a surface thereof.
2. Description of the Related Art
Percutaneous transluminal coronary angioplasty (PTCA) is a procedure for treating heart disease. A catheter assembly having a balloon portion is introduced percutaneously into the cardiovascular system of a patient via the brachial or femoral artery. The catheter assembly is advanced through the coronary vasculature until the balloon portion is positioned across the occlusive lesion. Once in position across the lesion, the balloon is inflated to a predetermined size to radially compress the atherosclerotic plaque of the lesion against the inner wall of the artery to dilate the lumen. The balloon is then deflated to a smaller profile to allow the catheter to be withdrawn from the patient""s vasculature.
A problem associated with the above procedure includes formation of intimal flaps or tom arterial linings which can collapse and occlude the vessel after the balloon is deflated. Moreover, thrombosis and restenosis of the artery may develop over several months after the procedure, which may require another angioplasty procedure or a surgical by-pass operation. To reduce the partial or total occlusion of the artery by the collapse of arterial lining and to reduce the chance of the development of thrombosis and restenosis, an implantable device, examples of which include stents and grafts, may be implanted.
Stents are scaffoldings, usually cylindrical or tubular in shape, which function to physically hold open and, if desired, to expand the wall of the vessel. Typically stents are capable of being compressed, so that they may be inserted through small cavities via catheters, and then expanded to a larger diameter once they are at the desired location. Examples in patent literature disclosing stents include U.S. Pat. No. 4,733,665 issued to Palmaz, U.S. Pat. No. 4,800,882 issued to Gianturco, and U.S. Pat. No. 4,886,062 issued to Wiktor.
Synthetic vascular grafts are vessel-like configurations that may be positioned into the host blood vessel as a replacement for a diseased or occluded segment that has been removed. Alternatively, a graft may be sutured to the host vessel at each end so as to form a bypass conduit around a diseased or occluded segment of the host vessel.
Although stents and grafts are significant innovations in the treatment of occluded vessels, there remains a need for administering therapeutic substances to the treatment site. Systemic administration of the therapeutic substance often produces adverse or toxic side effects for the patient. Local delivery of therapeutic substances, by contrast, provides a smaller overall dosage that is concentrated at a specific site. Local delivery can produce fewer side effects and achieve more effective results in many cases.
One technique for the local delivery of therapeutic substances employs medicated coatings on implantable devices. A typical method for medicating an implantable device includes applying a composition containing a polymer, a solvent, and a therapeutic substance to the implantable device using conventional techniques, such as spray-coating or dip-coating. The method further includes removing the solvent, leaving on the implantable device surface a coating of the polymer with the therapeutic substance impregnated in the polymer.
A recently developed type of stent includes a plurality of pores, called xe2x80x9cdepotsxe2x80x9d herein, that are formed in the outer surface of the stent. When such stents are coated using conventional methods, undesirable pockets of air can become trapped in the depots. Accordingly, a new coating method is needed for implantable devices having such depots.
The present invention provides methods by which implantable devices, such as stents and grafts, having a plurality of depots formed in a first surface thereof may be coated with therapeutic substances, among other possibilities.
An exemplary method within the present invention includes applying a composition including a polymer and a solvent to the first surface of the implantable device proximate to the depots. The application of the composition is performed at a first gas pressure. The method further includes applying a second gas pressure to the implantable device, wherein the second gas pressure is greater than the first gas pressure. Applying such an increased gas pressure drives the composition into the depots and eliminates, or at least reduces the size of, air pockets within the depots. The method also includes removing the solvent from the composition on the implantable device so that a stable, polymer-based coating is formed on the first surface and within the depots of the implantable device.
In some embodiments, the composition additionally includes a therapeutic substance. The therapeutic substance may be selected from antineoplastic, antimitotic, antiinflammatory, antiplatelet, anticoagulant, antifibrin, antithrombin, antiproliferative, antibiotic, antioxidant, and antiallergic substances and combinations thereof. Alternatively, the therapeutic substance may be a radioactive isotope or a radiopaque substance.
These and other aspects of the present invention may be better appreciated in view of the detailed description and drawings of the exemplary embodiments.